The high-temperature gas reactor control rod, which is used for high temperature gas reactors in nuclear electric power generation, has a structure in which a plurality of control rod elements are joined to each other in a vertical direction (up/down direction). Each of the control rod elements accommodates a neutron absorber such as B4C.
Conventionally, a metal-based high-temperature gas reactor control rod has been used for the control rod element serving as a means to accommodate a neutron absorber in a high temperature gas reactor. However, in the case of a large-scale high temperature gas reactor, in which the reactor core output power and the output power density are large and the temperature conditions are harsh, the control rod element made of a metallic material may cause the metal to melt, making it impossible to use the control rod repeatedly. This has been a technical problem. For this reason, in a large-scale high temperature gas reactor, a high-temperature gas reactor control rod made of C/C composite and a control rod element made of SiC/SiC composite, which can be used repeatedly, may be used as a control rod material that is an alternative to the metallic material.
Here, a known elevating and lowering mechanism for the high-temperature gas reactor control rod that is driven by a control rod drive apparatus has the following mechanism. A wire fixed to and integral with the control rod element is inserted through the interior of the inner cylinder of each of the control rod elements. By moving the wire upward and downward, the high-temperature gas reactor control rod is elevated and lowered. In view of such circumstances, a mechanism has also been proposed, in which a screw thread or an engaging portion is provided at a lower portion of an outer cylinder and an inner cylinder of each of control rod elements to connect the control rod element to each other (see Patent Document 1 below). Such a mechanism can somewhat inhibit the high-temperature gas reactor control rod from swaying. However, with the screw thread joining, stress such as tensile, bending, and shearing stress concentrates on the screw thread. For this reason, hanging load cannot be made large (in other words, the number of control rod elements joined is limited). Moreover, the thread may break with, for example, small shaking.
In view of this, a control rod having the following structure has also been proposed (see Patent Document 2 below). B4C powder is filled between the outer cylinder and the inner cylinder that use C/C composite and sintered. Connecting belts made of C/C are disposed in the outer cylinder of the control rod element, and the connecting belts are joined using a cruciform cross joint. The connecting belts adjacent to each other along the up/down direction are disposed so as to be twisted 90 degrees.